Asbestos, its incombustibility revered for centuries, was originally employed during the Stone Age as an additive to pottery. Later, the ancients, preparing for the king's cremation, frequently draped their rulers in funerary garments woven from this amazing fiber. During the Middle Ages, charlatans and magicians dazzled the peasantry with asbestos cloths that refused to burn. It wasn't until the late 19th Century, however, that asbestos received widespread industrial application. Today, the myriad of products containing this mineral are so numerous that they defy cataloging.
Unfortunately, asbestos is not without deletorious side effects. As early as two thousand years ago, the Greek geographer, Strabo, and the Roman naturalist, Pliny the Elder, described a sickness of the lungs found in slaves who wove asbestos into cloth and postulated that the adverse biological consequences evidenced by such slaves stemmed from their contact with this mineral. Outside of this passing reference to the disease, the effects of the lengthy exposure to this mineral went unnoticed. As asbestos became more prevalent, however, mysterious deaths and debilitating lung diseases were discovered in many workers. Originally attributed to ordinary dust and the poor ventilation of the factories, these infirmities were quickly ascribed to asbestos. This disease, entitled asbestosis, was later found to be a form of pneumoconiosis, a general term for all dust diseases of the lungs, and is characterized by pulmonary fibrosis.
While asbestos has been recognized as a serious health problem to workers in the field for at least 50 years, the voracious appetite for this material and the absence of adequate substitutes prevented its ban. Within the past few years though, the public's concern over its potential health hazards has reached a zenith. This interest stems in part from the widespread use of this material which brings nearly everyone within its spector. This, coupled with an understandable fear that one may be subjected to the fibers while unaware and will be unable to take necessary precautions, has aroused the public. Particularly frightening is a peculiar characteristic of this mineral. Because of its virtual indestructability, once inhaled, asbestos continues to react with the lungs for a lifetime. Recently, the medical profession has also noted a correlation between asbestos exposure and an increased incidence of cancer. Contact with asbestos has been found to cause, inter alia, mesothelioma, a frequently malignant tumor of the pleura. The potency of asbestos is so great that even those whose exposure to the material is minimal still suffer a risk of being stricken. The by-product of this concern, increasingly stringent controls placed on the use of asbestos, has triggered a quest for suitable substitutes embodying the beneficial aspects of resistance to heat, flexibility, and availability, without concomitant health problems. This search for replacements that have the diversity of functions found with asbestos has heretofore been unsuccessful.
In one particular industrial area, the use of asbestos was deemed particularly critical. Utility companies and other major industrial plants frequently have a series of high temperature conduits such as electric cables, control cables and pneumatic lines in close proximity. In utility companies large numbers of high voltage electric cables are separated by only a short distance. Because high voltages traverse these cables, they frequently operate at very high temperatures. Also, if one cable should ignite, the close proximity of the other cables presages a blazing inferno that quickly jumps from cable to cable, each cable in turn fueling the spreading conflagration.
A similar problem is found in many other industries, oil refineries for instance. There, control cables and pneumatic lines are subject to fires, and economic considerations often dictate that these conduits be close together as in the case of utility cables. Thus the need for a fire retardant composition.
While it is virtually impossible, in light of today's technology, to completely eliminate the prospect of a fire, it has been found that when a fire does break out, the damage can be minimized if the plant is quickly shut down, thereby preventing further fuel from reaching the flames. In a utility, termination of the electric current quickly lowers the temperature of the cables below the critical temperature and the fire can be extinguished at its inception. Critical to this method is prompt discovery of the blaze while it is still in its formative stages and a means of preventing the fire from spreading from its place of origin. One means of ensuring a small fire is to coat the cable with a flame-retardant composition that will prevent the spread of the flames. This enables plant operators to shut down operations before the fire rampages.
These compositions have frequently contained asbestos as one of the primary flame retardant constituents. This was primarily due to its widespread acceptance under nearly all building codes, its low cost, and its ease of application. While other compositions were not unknown, they frequently lacked the flexibility, acceptance, and low cost attendant to asbestos. Successful compositions employing other materials in addition to asbestos are disclosed in U.S. Pat. No. 3,642,531, U.S. Pat. No. 3,928,210 and U.S. patent application Ser. No. 687,345, now U.S. Pat. No. 4,064,359, the disclosures of which are incorporated by reference. While these compositions are in the form of an emulsion or mastic and thus do not have the free asbestos fibers that are presently the subject of debate by health authorities, nevertheless the regulatory climate throughout the world is such that use of the mineral is likely to be barred within a relatively short period of time irrespective of the form in which it is used.
The patents noted above disclose self-extinguishing fire protective compositions containing, inter alia, asbestos or other non-combustible fibers. An important characteristic of such fibers, however, is that they have high temperature resistance. Fibers having high temperature resistance are considerably more expensive than asbestos, however, and a manufacturer unconcerned about the deletorious effects of this substance has little incentive to employ these other fibers. Furthermore, many of these fibers lack the flexibility of asbestos as well as its high heat emissivity properties. Consequently, there is needed a fire retardant composition that embodies the beneficial attributes obtained with asbestos, including low costs, ease of application, flexibility, etc., but which does not contain asbestos and hence is totally free from concern as to any possible deletorious consequences.